The control of bleeding during surgery accounts for a major portion of the time involved in an operation. In particular, bleeding that occurs when tissue is incised obscures the surgeon's vision, delays the operation, and reduces the precision of cutting.
One technique for minimizing the bleeding of tissue as it is being severed is known as hemostatic surgery. This technique uses a heated instrument to contact bleeding tissue. The heat is transferred from the instrument to the incised (or torn) tissue to thermally reform collagen, thereby producing a thin collagenous film that seals over the severed blood vessels and capillaries, thereby reducing bleeding. Because heat is applied locally to tissue that contacts the heated region of the instrument, there is little tissue necrosis or damage that, if present, would retard healing.
One such hemostatic instrument is known as a hemostatic surgical scalpel. This scalpel has a sharp cutting edge similar to that of a conventional steel scalpel blade, and a heating element proximate to the cutting edge to heat the blade. During cutting, the scalpel blade is heated and the heat is transferred to the tissue being cut.
One commercial device using this technique is a hemostatic scalpel manufactured and sold by Hemostatix Medical Technology, Memphis, Tenn. and described in U.S. Pat. Nos. 3,768,482, 4,481,057, 4,485,810 and 5,308,311. This device uses a multi-segmented resistive heating element whereby the current flowing through each segment is individually controlled to maintain each segment, and hence the blade, within a narrow range of user-selected temperatures.
A drawback of previously known hemostatic heated scalpel blades has been the inability to deliver an adequate quantity of heat in close proximity to the cutting edge, to maintain a sharp durable cutting edge, and to be usable for sustained surgery under a wide variety of surgical cutting applications. Sufficient thermal delivery is critical to seal promptly the blood vessels and capillaries being severed. The quantity of heat that must be delivered increases with the rate at which the scalpel is being moved through the tissue and the degree of vascularization of the tissue. These conditions have limited the cutting rate and depth that the previously known devices can be used to hemostatically cut tissue.
Good surgical blades are commonly made of hard materials such as steels and martensitic stainless steels, but these materials generally have low thermal conductivity. High thermal conductivity materials are desirable for delivering the necessary heat, but typically do not maintain a sharp and durable cutting edge. Contact of the high thermal conductivity blades with the corrosive biological fluids and operation at elevated temperatures combine to dull the cutting edges of such blades prematurely. Moreover, they also conduct large amounts of heat to the handle of the blade, making it uncomfortable for the surgeon to hold the instrument during surgery.
Attempts to use other blade materials have been made without any apparent success, e.g., ceramic blades as described in Shaw U.S. Pat. No. 3,768,482, Johnson U.S. Pat. No. 4,219,025, Lipp U.S. Pat. No. 4,231,371, and high thermal conductivity materials treated to have hardened cutting edges as described in U.S. Pat. No. 4,770,067. These devices similarly lack the combination of desirable thermal transfer properties and a durable sharp cutting edge.
Other types of hemostatic scalpel devices having non-segmented heating elements for heating the sharp scalpel blades are described in a U.S. Pat. Nos. 4,207,896, 4,091,813 and 4,185,632. Attempts have been made to increase the delivery of heat to the tissue by using thick-film, glass-based dielectric, resistive heater and electrical lead layers printed on the metallic blade as described in U.S. Pat. No. 5,308,311. However, this approach requires heating the blade to greater than 400° C. for up to 60 minutes to melt and adhere the multiple glass dielectric lead layers. This necessary processing time at temperatures unavoidable reduces the hardness of the cutting edge due to the effect known as annealing or tempering. As a consequence of the reduced hardness, these scalpel blades cannot reach the desired level of sharpness and/or durability required for surgical procedures. In addition, the reduced level of hardness results in a more rapid rate of edge wear or dulling during the course of a surgical procedure. Furthermore, the use of thick-film, glass-based dielectric, resistive heater and electrical lead layers is not well suited to smaller blade sizes such as the well known No. 11 and No. 12 surgical blade types since the surface area required for the leads reduces the available area for the resistive heater resulting in excessive heat fluxes through the dielectric layer. Also, there is the need for scalpel blades with an extended length in order to access surgical sites such as the tonsils for tonsillectomy procedures. However, the glass-based inks are susceptible to cracking due to the long length of the blade and the associated thermal expansion mismatch between the glass-based thick-film and the blade substrate.
Also, the metallic blade as described in U.S. Pat. No. 5,308,311 utilizes an alumina dispersion strengthened copper (GlidCop AL 15 manufactured by Gibraltar Industries/SCM Metals Corporation, Buffalo, N.Y.) layer to provide the needed thermal conductance between the heater region and the cutting edge of the blade. As a result of the limitation of the manufactured length of alumina dispersion strengthened copper strip, the roll-bonding of this alumina dispersion strengthened copper to the cutting edge material is limited to short lengths of roll bonding and associated poor production yields. In addition, the price of the alumina dispersion strengthened copper is more than 20 times that of ordinary oxygen-free, hard copper. The prior use of dispersion strengthened copper was necessary due to the essential heat treatment of the cutting edge which involves heating the entire laminate to temperatures of over 1000° C. for more than 30 minutes. Conventional high thermal conductivity materials such as oxygen-free hard copper will become completely annealed under these heat treatment conditions making them too weak to maintain the shape and flatness of the scalpel blade.
In addition, prior art handles which support the scalpel blade have been manufactured with an integral cable. The high cost of the cable containing up to 10 or more conductors and the need for making 10 or more soldered interconnections between the cable and the handle makes the handle expensive and more susceptible to failure.
Accordingly, there is a continuing need to provide a sharp, durable scalpel blade capable of delivering sufficient thermal energy to the tissue to cause hemostasis under a wide variety of operating conditions. In addition, there is a need to simplify the complexity of the handle construction to increase its reliability and reduce the frequency of the replacement of the handle assembly.